How to truncate milliseconds off of a .NET DateTime

Question

I'm trying to compare a time stamp from an incoming request to a database stored value. SQL Server of course keeps some precision of milliseconds on the time, and when read into a .NET DateTime, it includes those milliseconds. The incoming request to the system, however, does not offer that precision, so I need to simply drop the milliseconds.

I feel like I'm missing something obvious, but I haven't found an elegant way to do it (C#).

Answer 1

The following will work for a DateTime that has fractional milliseconds, and also preserves the Kind property (Local, Utc or Undefined).

DateTime dateTime = ... anything ... dateTime = new DateTime(     dateTime.Ticks - (dateTime.Ticks % TimeSpan.TicksPerSecond),      dateTime.Kind     ); 

or the equivalent and shorter:

dateTime = dateTime.AddTicks( - (dateTime.Ticks % TimeSpan.TicksPerSecond)); 

This could be generalized into an extension method:

public static DateTime Truncate(this DateTime dateTime, TimeSpan timeSpan) {     if (timeSpan == TimeSpan.Zero) return dateTime; // Or could throw an ArgumentException     if (dateTime == DateTime.MinValue || dateTime == DateTime.MaxValue) return dateTime; // do not modify "guard" values     return dateTime.AddTicks(-(dateTime.Ticks % timeSpan.Ticks)); } 

which is used as follows:

dateTime = dateTime.Truncate(TimeSpan.FromMilliseconds(1)); // Truncate to whole ms dateTime = dateTime.Truncate(TimeSpan.FromSeconds(1)); // Truncate to whole second dateTime = dateTime.Truncate(TimeSpan.FromMinutes(1)); // Truncate to whole minute ...